Medical needles such as those used for injection, infusion, and blood collection generally possess sharp blade tips to puncture into skins of living bodies. Use of such needles in repetition is accompanied with risks of transmitting pathogens from a body to another, and it is now common that needles are used once and discarded.
There are, however, a number of people who handle the needles, including those who actually use the needles such as doctors and nurses, and those who handle the needles until final disposition of the needles. There is a potential danger that the needle tip accidentally injures the users before the use and particularly after the use, or accidentally injures those who handle the needles thereafter. The needles before use are sterile, but there arises risks of infection by transfer of pathogens through a medium such as blood when a needle is once used through the skin of a living body, and the tip then accidentally injures one or more other persons.
It is therefore desirable that such accidental puncturing is prevented throughout the life of needles from a time before the use until they are finally demolished. Needles for medical uses are generally distributed with their tips protected by caps. The caps are put on the tips again after the use for protecting the tips. It happens commonly, however, that the used needles are thrown away without the caps. The Japanese patent laid-open publication JPA62-72367 proposes safety devices for hypodermic needle or the like that connects a hypodermic needle with a sleeve. The sleeve slides along the needle after the use and is locked where the sleeve completely covers the needle.
As discussed in the foregoing, needles for medical uses bear a high risk of accidental puncturing from a time before the use until they are finally demolished.